1. Field of the Invention
The present invention relates to a novel onium salt compound having an —SO2 structure, —OSO2— structure, or —O—S(O)R2 structure bonded to an aromatic hydrocarbon group or a heterocyclic group, a photoacid generator comprising the onium salt compound, and a positive-tone radiation-sensitive resin composition comprising the photoacid generator useful for microfabrication represented by the manufacture of integrated circuit devices.
2. Description of Background Art
In the field of microfabrication represented by the manufacture of integrated circuit devices, lithographic technology enabling microfabrication with a line width of 0.30 μm or less has been demanded in order to increase the degree of integration in recent years. In a conventional lithographic process, near ultraviolet rays such as i-line radiation have been generally used. However, it is difficult to perform microfabrication with a line width of sub-quarter micron using near ultraviolet rays. Therefore, in order to enable microfabrication with a line width of 0.30 μm or less, utilization of radiation with a shorter wavelength has been studied.
As radiation with a shorter wavelength, deep ultraviolet rays represented by a line spectrum of a mercury lamp and an excimer laser, X-rays, electron beams, and the like can be given. Of these, deep ultraviolet rays such as a KrF excimer laser (wavelength: 248 nm), an ArF excimer laser (wavelength: 193 nm), an F2 excimer laser (wavelength: 157 nm), or EUV (wavelength 13 nm), and electron beams have attracted attention.
As a radiation sensitive resin composition applicable to short wavelength radiations, a number of compositions utilizing a chemical amplification effect between a component having an acid functional group protected with an acid-dissociable group and a photoacid generator which generates an acid upon irradiation (hereinafter referred to as “exposure”) has been proposed. Such a composition is hereinafter referred to as a chemically-amplified radiation sensitive composition. For example, Japanese Patent Application Laid-open No. 59-45439 discloses a chemically-amplified radiation-sensitive composition containing a polymer of which the carboxyl group or phenolic hydroxyl group is protected with a t-butoxycarbonyl group and a photoacid generator. This composition utilizes the effect of the polymer to release the t-butoxycarbonyl group by the action of an acid generated by exposure to form an acidic functional group such as a carboxylic group or a phenolic hydroxyl group, which renders an exposed area on a resist film readily soluble in an alkaline developer.
However, most of the photoacid generators currently used for conventional chemically-amplified radiation-sensitive compositions have only insufficient sensitivity. A sulfonium salt compound, which has been regarded as having the highest sensitivity, exhibits only very low base resistance, posing a serious problem of storage stability of the composition. The type of acid diffusion inhibitor, which is a basic additive for improving process stability as a resist, is also limited.
Therefore, development of a highly sensitive, more excellent photoacid generator exhibiting superior base resistance and excellent storage stability is strongly desired.
Japanese Patent Application Laid-open No. 63-36332 and J. of Polymer Sci., Polymer Chemistry Edition, Vol. 18, p. 2697–2714 (1980) disclose that a sulfonium salt compound having a sulfonyl structure bonded with an aromatic ring is useful as a photoinitiator due to a cation mechanism. However, no sulfonium salt compound having a sulfonyl structure bonded with an alicyclic ring has been synthesized heretofore.
The present invention has been completed in view of the above situation and has an object of providing a novel onium salt compound responsive to active radiations such as deep ultraviolet rays represented by a KrF excimer laser, ArF excimer laser, F2 excimer laser, and EUV, as well as to electron beams, having superior storage stability, suitable for a photoacid generator used for a radiation-sensitive resin composition as a high sensitivity, high resolution chemically-amplified photo resist, a photoacid generator comprising the onium salt compound, and a positive-tone radiation-sensitive resin composition comprising the photoacid generator.